Project 1. Oligonucleotide fingerprinting analysis in conjunction with immunological analysis of several recombinant viruses generated both in vitro and in vivo from parental viruses with different oncogenic potential (between different Rauscher-MuLV ts and BALB:virus-2) enabled us to establish for the first time in the mouse leukemia system the exact order of the known leukemia virus genes. Project 2. In order to study the evolutionary pathways of mouse endogenous type-C viruses with respect to a common progenitor, we studied the distribution of different classes of inducible viruses among inbred strains of mice from diverse geographical areas.